Formula MassesFormula mass or formula weight- the sum of the atomic masses of all the atoms in the formula unit.Treat the formula like an algebra expression. The mass unit for individual atoms or molecules is amu.Also called Molecular mass or Molecular formulaFor ionic compounds its called Formula mass, e.g NaCl; NaNO3

ExampleNi(ClO2)2Nickel chlorite start inside parentheses-(ClO2)multiply each atom's mass by its subscriptCl = 35.5 *1 and O2 = 16.0*2get the sum inside parentheses(ClO2) = (35.5 + 32.0) = 67.5multiply by subscript that follows parentheses(ClO2)2 = 67.5*2 = 135.0add mass of additional element(s)Ni = 58.7 Ni(ClO2)2 = 58.7 + 135.0 = 193.7 amu

Example 1

Percent Composition (by mass)

Apply the formula-% x = (mass of x / total mass) * 100%

Example 2

The Mole

The mole is the fundamental measure of quantity to substance (abbreviated mol).

Avogadros number 6.0221367 x 1023 thingsMole defined as number of 12C atoms in exactly 12 g of 12C, equal to 6.02 x 1023 particlesOne mole of a substance contains 6.02 x 1023 particles of that substance.

Molar mass (MM) is the mass of one mole of a substance units g/mol .1 amu = 1.66 x 10-23 g

Example 3

Example 4

The Chemical Formula for a compound gives the ratio of atoms of each element in the compound to atoms of every other element in the compound.Also it gives the ratio of moles of atoms of each element in the compound to moles of atoms of every other element in the compound.

Example:H2O has 2 atoms of H for every atom of OAlso has 2 mol of H for every mol of O atom

Example 5

Empirical Formula

Is a formula that gives the lowest whole-number ratio of atoms of all the elements.For example:The empirical formula of the simple sugar fructose, C6H12O6 is CH2O So the ratio of C: H : O atoms in the formula is 1 : 2 : 1

Example 6